Apparatus for monitoring the state of a protective device of a machine

ABSTRACT

An apparatus ( 1 ) for monitoring the state of a protective device ( 2 ) of a machine ( 4 ) in particular is a safety switch for monitoring the closed state of a protective door or the like. The apparatus ( 1 ) has a switch housing ( 22 ) with a switch head ( 24 ) and an actuator ( 8 ). In the closed state of the protective device ( 2 ), the actuator interacts with the switch head ( 24 ) and, as a result, the closed state of the protective device ( 2 ) can be signaled. The apparatus ( 1 ) has a tumbler device ( 20 ) with a tumbler element ( 30 ) mounted movably in the apparatus ( 1 ) and by which the closed state of the protective device ( 2 ) can be locked releasably. The tumbler device ( 20 ) has at least one permanent magnet ( 34 ). By the magnetic force, the tumbler element ( 30 ) can be fixed in a first position when the power supply to the apparatus ( 1 ) is switched off, in which first position the tumbler device ( 20 ) locks the closed state of the protective device ( 2 ), and/or can be fixed in a second position, in which the tumbler device ( 20 ) does not lock the closed state of the protective device ( 2 ).

FIELD OF THE INVENTION

The invention relates to an apparatus for monitoring the state of aprotective device of a machine. In particular, a safety switch monitorsthe closed state of a protective door or the like, having a tumblerfunction for the protective device.

BACKGROUND OF THE INVENTION

DE 43 28 297 C1 discloses a safety switch having a switch head receivingan actuator fixed, for example, on the protective door of a protectivedevice to turn a ratchet wheel. Within the switch housing, a contactplunger is held in contact with the peripheral surface of the ratchetwheel. At an angle of rotation corresponding to the closed position ofthe protective door, the contact plunger engages a catch depressionprovided for this purpose on the peripheral surface of the ratchetwheel, and thus, closes a contact pair. In this way, the inserted stateof the actuator and, accordingly, the closed position of the protectivedoor can be electrically signaled.

For many applications, for example, for protective hoods on machinetools or the like, in addition it is necessary for the safety switch tomake available a tumbler function, i.e., for the actuator to be lockablein the switch head, in particular to be lockable with respect to beingrouted out of the switch head, and thus for the protective device to belockable in the closed state. In the prior art safety switch, thecontact plunger is held in the catch depression, loaded by spring forceor magnetic force, and thus blocks rotary motion of the cam disk.

For some applications, it is necessary, for example, for reasons of fireprotection, for instance, when the electrical voltage supply of themachine is turned off in case of a fault, for the protective device tobe locked in the closed state, for example, in the closed position ofthe protective door. This need engenders the problem that in theotherwise de-energized state of the apparatus, for example, on theoccasion of cleaning activities on the weekend, in an unintentional orinadvertent closing of the protective device the tumbler device isactivated. The protective device is then locked or held then in theundesirable closed state. The requirement for “tumbler in thede-energized state” and simultaneous “prevention of activation oftumbler in the de-energized state” therefore constitutes an apparentlyinsurmountable contradiction for generic apparatus.

DE 10 2004 047 574 A1 discloses a solution to this problem in which ablocking element is mounted to be transversely movable to the tumblerelement and in a position fixing the tumbler element positively toengage a recess in the tumbler element. This known solution dictates alarger-scale design of the apparatus.

SUMMARY OF THE INVENTION

An object of the invention is to provide an apparatus for monitoring thestate of a protective device of a machine overcoming the disadvantagesof the prior art. In particular, the object of the invention is toprovide an apparatus with a tumbler device made to implement both thefunction “tumbler in the de-energized state” and the function“prevention of activation of tumbler in the de-energized state” with areduced design size. In one embodiment, an exact tumbler is to bepermanently and reliably ensured, and thereby, large tumbler forces areto be made available economically and durably with structurally simplemeans. Production, installation and maintenance of the apparatus are tobe simplified to save time and money.

This object is basically achieved by an apparatus having at least onepermanent magnet whose magnetic force is sufficient to fix the tumblerelement optionally against the action of another applied force, forexample, by a spring element to the tumbler element. In one embodimentthe permanent magnet fixes the tumbler element in a first position inwhich the tumbler device locks the closed state of the protectivedevice, for example, by the actuator being locked in the switch head andthe actuator cannot be guided out of the switch head, if the tumblerelement is in or near this first position when the power supply of theapparatus is turned off.

In one embodiment, the permanent magnet fixes the tumbler element in asecond position in which the tumbler device does not lock the closedstate of the protective device if the tumbler element is in or near thissecond position at the instant the power supply of the apparatus isturned off.

In another embodiment, the permanent magnet can fix the tumbler elementboth in the first position and in the second position, depending on inwhich position the tumbler element is located at the instant the powersupply of the apparatus is turned off.

There can also be two or more permanent magnets, in which the tumblerelement can be fixed in the first position by a first permanent magnet,and the tumbler element can be fixed in the second position by a secondpermanent magnet.

For the interaction of the tumbler element with the permanent magnet,the tumbler element is made to be magnetizable at least in sections andhas, for example, a first, preferably cylindrical, section of amagnetizable material. The tumbler element can be dynamically connectedto the plunger at the same time for actuating an electrical switchingelement of the apparatus. In particular, it can be part of the plungeror can form a section of the plunger, or the plunger and the tumblerelement are made in one piece.

In one embodiment, the tumbler element is mounted to be linearly movablein the apparatus and in particular in the tumbler device.

For example, the tumbler element can have the form of an elongatedcylinder and can be mounted to be movable along its longitudinal axis.In one embodiment, the tumbler element has sections with differingradial extensions.

In one embodiment, the permanent magnet extends around the tumblerelement and is preferably made ring-shaped. The permanent magnet can bemagnetized axially or radially relative to the direction of motion ofthe tumbler element. The magnetic flux caused by the permanent magnet atleast partially flows and at least in the first or second fixed positionthrough the tumbler element, and thus, exerts the force fixing thetumbler element.

In one embodiment, the permanent magnet has a capture region. As soon asthe tumbler element is moved into the capture region, the permanentmagnet applies a force to the tumbler element by which the tumblerelement is transferred into the first or second position and is fixedtherein. The geometrical arrangement of the permanent magnet relative tothe tumbler element is preferably chosen such that due to the tumblerelement's entering the capture region of the permanent magnet, the forcetransferring the tumbler element into the fixing position becomesgreater over the course of the transfer motion.

In one embodiment, the tumbler element has at least one electromagnet,by whose energizing the fixing of the tumbler element can be cancelled.For this purpose, the electromagnet can be energized, in particular canbe energized with a direct current in a suitable current direction, suchthat the magnetic flux caused by the electromagnet reduces the magneticflux caused by the permanent magnet or even more or less completelycompensates for it. In this way the force applied by the permanentmagnet to the tumbler element is no longer sufficient to fix the tumblerelement in position. The tumbler element can then be moved out of thefixed position, for example, as a result of the force applied by anenergy storage mechanism.

In one embodiment, the magnetic force applied to the tumbler element canbe increased by energizing the electromagnet. In this way, for example,the tumbler element as a result of the magnetic force of theelectromagnet can be moved into the capture region of the permanentmagnet, if necessary even against the action of the energy storagemechanism. The energy storage mechanism is made, for example, as acompression spring and applies a force to the tumbler element againstthe magnetic force of the permanent magnet.

In one embodiment, amplification or attenuation of the magnetic forceapplied by the permanent magnet to the tumbler element is caused byswitching the direction of current flow through the electromagnet.Energizing can take place with a continuous current. The current valuecan be adjustable and controllable, for example, to be able to vary themagnetic force applied by the electromagnet to the tumbler element. Forexample, the electromagnet can be briefly supplied with an overcurrentto guide the tumbler element into the capture region of the permanentmagnet and/or to route the tumbler element out of the capture region.Energizing can also take place pulsed, in which the amplitude of thecurrent pulses and/or the duration of the current pulses can becontrollable to be able to vary the magnetic force applied by theelectromagnet to the tumbler element.

In one embodiment, by energizing the electromagnet, the tumbler elementcan be transferred from the first position into the second positionand/or can be transferred from the second position into the firstposition. To do this, in the simplest case a single electromagnet can beused and energizable in one current direction or the other. In oneembodiment the apparatus has two or more electromagnets. By energizing afirst electromagnet the tumbler element can be transferred from thefirst position into the second position, and by energizing the secondelectromagnet the tumbler element can be transferred from the secondposition into the first position. At the same time, the magnetic forceapplied by the permanent magnet to the tumbler element can be varied, inparticular, reduced, by one of the electromagnets.

In one embodiment the electromagnet can be made as a coil in whoseinterior the tumbler element is mounted to be longitudinally movable.The permanent magnet is located bordering the electromagnet, inparticular in the core of the electromagnet which routes the magneticflux. In one embodiment the permanent magnet is located in the yoke ofthe electromagnet.

Other objects, advantages and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, discloses preferredembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a schematic plan view of the overall arrangement with anapparatus according to the invention;

FIG. 2 is a detailed plan view in section of an apparatus according to afirst embodiment of the invention;

FIGS. 3 to 8 are partial, detailed plan views of different states of theapparatus of the embodiment of FIG. 2;

FIG. 9 is an enlarged, partial plan view of an apparatus according to asecond embodiment of the invention; and

FIG. 10 is an enlarged, partial plan view of an apparatus according to athird embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic plan view of the overall arrangement of anapparatus 1 according to the invention for monitoring the state of aprotective device 2 of a machine 3, in particular of the closed state ofa protective door. A space separation device can be locked in order, forexample, to protect operators against hazards posed by the machine 3 inoperation. The device 2 has a first part 4, for example, a frame for theprotective device 2. The first part 4 has an opening 5 which can beclosed by a movable second part 6, for example, a protective door,according to the double arrow 10, relative to the first part 4. Secondpart 6 is mounted to be movable by bearing elements 11. The apparatus 1has a safety switch comprising a switch element 7 located preferably onthe stationary first part 4 of the protective device 2 and comprises anactuator 8 located on the movable second part 6.

FIG. 2 is a detailed plan view of a first embodiment of the apparatus 1with a switch housing 22 and a switch head 24 attached to housing 22.For inserting the actuator 8 (FIG. 1), switch head 24 has two insertionchannels 26, 28 located essentially equidistantly from one edge of theessentially cubic switch head 24 and aligned at a right angle to oneanother. In the switch head 24, a ratchet wheel 12 is mounted to rotatearound an axis aligned perpendicular to the plane of the drawing. Thewheel projects into the two insertion channels 26, 28 and can be rotatedby inserting the actuator 8 into one of the insertion channels 26, 28.On the ratchet wheel 12, a plunger 14 is held in contact by an energystorage mechanism 16 mounted in the switch housing 22. The contactplunger 14 actuates an electrical switching element 18 located in thesection of the switch housing 22 opposite the switch head 24.

Between the switch head 24 and the switching element 18, a tumblerdevice 20 is located in the switch housing 22 and has a tumbler element30 mounted to be movable along its longitudinal axis. The tumblerelement is cylindrical in sections and formed, in particular, in athickened section at least partially from a magnetizable material. Onits end facing the switch head 24, the plunger element 30 is positivelyconnected to the first section of the plunger 14 which is in contactwith the ratchet wheel 12 in its further extension. On the end facingthe switching element 18, the tumbler element 30 has a tapered orreduced diameter cylindrical section in contact with the actuatingplunger 32 of the switching element 18.

Energy storage mechanism 16 is supported on one shoulder of the tumblerelement 30 formed by the transition from the tapered cylindrical sectionto the thickened section of the tumbler element 30 having themagnetizable material. Proceeding from the tapered section, thetransition initially is right-angled to then undergo transition into aconical section which on its widened end undergoes transition into thesubsequent thickened section of the tumbler element 30.

The tumbler device 20 has a permanent magnet 34 magnetized in the axialdirection relative to the direction of motion of the tumbler element 30and inserted into a pole core 36 which conducts the magnetic flux. Thepermanent magnet 34 and the pole core 36 are connected to one anotherand are separated only by a small air gap from the tumbler element 30,in particular from the thickened section of the tumbler element 30. Thisstructure results in a magnetic flux indicated by the field line 38 andentering the tumbler element 30 from the permanent magnet 34 directlyor, by way of the pole core 36. In sections it penetrates the tumblerelement 30 and then again enters the pole core 36 or the permanentmagnet 34 directly. In this way, the permanent magnet 34 applies amagnetic force to close the air gap to the tumbler element 30 and thusto counteract the force applied by the energy storage mechanism 16 andfixes the tumbler element 30 in the illustrated position in which thetumbler device 20 does not lock the ratchet wheel 12, so that anactuator 8 could be inserted into the switch head 24 without the tumblerbeing activated.

Radially relative to the direction of motion of the tumbler element 30outside the permanent magnet 34, an electromagnet 40 is located and canbe energized in a controllable manner, the direction of current flowbeing reversible. In particular, the direction of current flow can bechosen by the electromagnet 40 either such that the resulting magneticflux counteracts the magnetic flux caused by the permanent magnet 34, orcan be selected such that the magnetic flux of the electromagnet 40amplifies the magnetic flux of the permanent magnet 34.

FIGS. 3 to 8 show different states of the embodiment of FIG. 2. Of theapparatus 1, in FIGS. 3 to 8 only the upper part of the switch housing22 is shown enlarged each time; the lower part of the switch housing 22is made as is shown in FIG. 2.

FIG. 3 shows the initial state, illustrated in FIG. 2, in which theactuator 8 is not inserted into the switch head 24 and the tumblerelement 30 is fixed by the magnetic force of the permanent magnet 34 inthe position in which the tumbler element 30 does not lock the ratchetwheel 12. This state is also maintained when the power supply of theapparatus 1 is turned off. It is a stable state since the magnetic forceapplied by the permanent magnet 34 is greater than the force of theenergy storage mechanism 16 acting in the opposite direction on thetumbler element 30.

If, proceeding from the position shown in FIG. 3, the actuator 8 isinserted into the switch head 24, the ratchet wheel 12 consequently isturned approximately 90° counterclockwise from FIG. 3 so that for theratchet wheel 12 the position shown in FIG. 4 results. The electromagnet40 still is not energized so that the tumbler element 30 remains in itsfixed position and the ratchet wheel 12 is not blocked. Accordingly, thetumbler device does not lock the closed position of the protectivedevice 2. Rather the protective door could be opened again and theactuator 8 could be guided out of the switch head 24.

If the electromagnet 40 is energized in a suitable current direction,the magnetic flux shown by the field line 42 in FIG. 5 weakens thefixing action of the permanent magnet 34 on the tumbler element 30because the magnetic flux caused by the electromagnet 40 in the regionof the tumbler element 30 is directed opposite the magnetic flux causedby the permanent magnet 34. In this way the magnetic action of thepermanent magnet 34 on the tumbler element 30 is cancelled or in anycase reduced so dramatically that at this point the force applied by theenergy storage mechanism 16 prevails and the tumbler element 30 is movedinto the position shown in FIG. 5 in which the tumbler element 30 or itsaxial extension engages a recess 13 in the ratchet wheel 12 by theplunger 14 and blocks said ratchet wheel against further rotary motion.

In this state the tumbler element 30 is fixed in the position in whichthe tumbler device 20 locks the closed state of the protective device 2.This state is also maintained when the energizing of the electromagnet30 is turned off, as follows from FIG. 6. In this case the permanentmagnet 34 is still acting, and a magnetic flux through the tumblerelement 30 may also occur, but it is too small to cause the tumblerelement 30 to move against the action of the energy storage mechanism 34due to the fact that the thickened section of the tumbler element 30 islocated outside the capture region of the permanent magnet 34.

Only by energizing the electromagnet 40 in a suitable direction as isshown by the field line 42 in FIG. 7 can a magnetic force which isgreater than the force of the energy storage mechanism 16 be applied tothe tumbler element 30. The tumbler element 30 is then moved in thedirection of the permanent magnet 34, in particular, into the captureregion of the permanent magnet 34 in which the force applied by thepermanent magnet 34 to the tumbler element 30 is sufficient to transferit into the position shown in FIG. 7 and fix it there, even when theenergizing of the electromagnet 40 is turned off, as is shown in FIG. 8.In this state the actuator 8 can be routed out of the switch head 24 sothat in turn the initial state shown in FIG. 3 results.

FIG. 9 shows an enlarged extract of a second embodiment of the apparatus101 and, in particular, of the tumbler device 120 in the region of theelectromagnet 140. The winding of the electromagnet 140 is surrounded bya magnetic core 144 which conducts the magnetic flux well, and in whichthe magnetic flux is guided, as shown by the field lines 142. On oneside facing the tumbler element 130, on the electromagnet 140 there is apermanent magnet 134 polarized relative to the direction of motion ofthe tumbler element 130 in the axial direction and, accordingly, themagnetic flux also flows through it. The permanent magnet 134 isembedded on its two axial end sides in the pole core 136 which is partof the magnetic core 144.

FIG. 10 shows an enlarged extract through a third embodiment of theapparatus 201 and, in particular, of the tumbler device 220 in theregion of the electromagnet 240. The permanent magnet 234 is located onone side which adjoins the side of the permanent magnet 240 facing thetumbler element 230. The permanent magnet 234 is radially magnetizedrelative to the direction of motion of the tumbler element 230. The polecore 236 forms a part or section of the core 244 which conducts themagnetic flux. The permanent magnet 234 is in turn located in themagnetic yoke of the electromagnet.

1. A safety switch for monitoring a state of a protection device,comprising: a switch housing with a switch head; an actuator interactingwith said switch head in a closed state of the protective device tosignal the closed state of the protective device; and a tumbler devicewith a tumbler element axially movably mounted in said switch housingand releasably locking said actuator with said switch head in the closedstate of the protective device, said tumbler device having at least onepermanent magnet generating a magnet force retaining said tumblerelement in at least one of a first position in which said tumbler devicelocks the closed state of the protective device and a second position inwhich said tumbler device unlocks the closed state of the protectivedevice when a power supply to the safety switch is turned off, saidtumbler device having at least one electromagnet generating a magneticforce when energized to transfer said tumbler element between said firstand second positions, said permanent magnet being located in an axialdirection within axial extents of said tumbler element and saidelectromagnet such that said permanent magnet, said tumbler element andsaid electromagnet overlap in a radial direction, magnetic flux of saidelectromagnet weakening the magnetic force of said permanent magnet onsaid tumbler element by said magnetic flux of said electromagnet beingopposite magnetic flux of said permanent magnet to allow said tumblerelement to move to the other of the first and second positions.
 2. Asafety switch according to claim 1 wherein said permanent magnet is ringshaped and extends about said tumbler element.
 3. A safety switchaccording to claim 1 wherein a spring biases said tumbler element andapplies a biasing force toward one of said first and second positions;and said permanent magnet counteracts said biasing force.
 4. A safetyswitch according to claim 1 wherein said permanent magnet has a captureregion and retains said tumbler element by said magnet force thereofinto one of said first and second positions as soon as said tumblerelement enters said capture region.
 5. A safety switch according toclaim 1 wherein said electromagnet generates the magnetic force thereofin a pulsed manner.
 6. A safety switch according to claim 1 wherein saidelectromagnet has a yoke causing the magnet flux thereof; and saidpermanent magnet is located in said yoke.
 7. A safety switch accordingto claim 1 wherein said permanent magnet retains said tumbler device insaid second position against a biasing force of a spring toward saidfirst position in a capture region of said permanent magnet.
 8. A safetyswitch according to claim 7 wherein said electromagnet generating themagnetic force thereof when energized that cancels said magnetic forceof said permanent magnet on said tumbler element.